Records in Dart

What are Records?

Records (introduced in Dart 3.0) are anonymous immutable aggregate types. They bundle multiple values together without creating a full class. Think of them as lightweight, typed tuples.

Syntax

// Create a record
(int, String) person = (25, 'Alice');
print(person.$1);  // 25  (positional access)
print(person.$2);  // Alice

// Record type annotation
(double, double) coordinates = (37.7749, -122.4194);

// Return multiple values from a function
(int, String) getUser() => (1, 'Bob');

Named Fields

// Named field records
({String name, int age, String email}) user = (
  name: 'Alice',
  age: 30,
  email: 'alice@example.com'
);

print(user.name);   // Alice
print(user.age);    // 30
print(user.email);  // alice@example.com

// Mix of positional and named
(int, {String name, bool isAdmin}) adminUser = (1, name: 'Bob', isAdmin: true);
print(adminUser.$1);         // 1
print(adminUser.name);       // Bob
print(adminUser.isAdmin);    // true

Destructuring Records

var (x, y) = (10, 20);
print('x=$x, y=$y');  // x=10, y=20

var (:name, :age) = (name: 'Alice', age: 30);
print('$name is $age');  // Alice is 30

// In a for loop
List<(String, int)> scores = [('Alice', 95), ('Bob', 87), ('Charlie', 92)];
for (var (name, score) in scores) {
  print('$name: $score');
}

Example: Multi-value Returns

({double min, double max, double average}) stats(List<double> numbers) {
  if (numbers.isEmpty) return (min: 0, max: 0, average: 0);
  var sorted = [...numbers]..sort();
  var sum = numbers.reduce((a, b) => a + b);
  return (
    min: sorted.first,
    max: sorted.last,
    average: sum / numbers.length,
  );
}

void main() {
  var result = stats([5.0, 3.0, 8.0, 1.0, 9.0]);
  print('Min: $${result.min}');      // Min: 1.0
  print('Max: $${result.max}');      // Max: 9.0
  print('Avg: $${result.average}');  // Avg: 5.2
}

Min: 1.0
Max: 9.0
Avg: 5.2

🧠 Quiz

Summary

Records are anonymous immutable value types introduced in Dart 3.0. Use (Type1, Type2) for positional fields (accessed via .$1, .$2) and ({FieldType name}) for named fields. Records are great for returning multiple values from functions without creating a class.